DESCRIPTION (Adapted from Investigator's Abstract) The processing and presentation of antigens by major histocompatibility complex class I molecules is critical for the recognition and destruction of virally-infected cells and tumor cells. The processing of antigens involves the intracellular degradation of the antigen by the ubiquitin-proteasome pathway, transport of the peptides into the endoplasmic reticulum, association with class I molecules, and expression on the cell surface to be recognized by cytotoxic T cells. The long-term objective of this project is to further elucidate the mechanisms of class I antigen processing. Here the investigators propose (1) To study the role of cytosolic heat shock proteins in class I antigen processing through in vitro peptide binding and transport assays. They want to show that heat shock proteins can modulate peptide binding and/or transport by the transporter associated with antigen processing. This will provide evidence for peptide transfer role cytosolic heat shock proteins in the class I processing pathway. (2) To develop a system for the measurement of the ubiquitylation of viral antigens. This will allow determination of the extent and importance of ubiquitylation in antigen presentation, and to ultimately study what regulates antigen ubiquitylation. (3) To develop an in vitro assay for the measurement of peptide trimming/degradation events in the endoplasmic reticulum. They wish to use tricine gels to detect the degradation of labeled antigenic peptides in microsomes, and to partially characterize the associated proteolytic activity. A detailed understanding of the major histocompatibility complex class I antigen processing pathway is crucial for the development of preventative and therapeutic strategies for cancer, and diseases associated with viral infection.